My First React App — Intro to React 2021

Before Starting this tutorial

What is React

Getting Started

Getting Familiar with what’s inside

Looking at index.html

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<link rel="icon" href="%PUBLIC_URL%/favicon.ico" />
<meta name="viewport" content="width=device-width, initial-scale=1" />
<meta name="theme-color" content="#000000" />
<meta
name="description"
content="Web site created using create-react-app"
/>
<link rel="apple-touch-icon" href="%PUBLIC_URL%/logo192.png" />
<!--
manifest.json provides metadata used when your web app is installed on a
user's mobile device or desktop. See https://developers.google.com/web/fundamentals/web-app-manifest/
-->
<link rel="manifest" href="%PUBLIC_URL%/manifest.json" />
<!--
Notice the use of %PUBLIC_URL% in the tags above.
It will be replaced with the URL of the `public` folder during the build.
Only files inside the `public` folder can be referenced from the HTML.
Unlike "/favicon.ico" or "favicon.ico", "%PUBLIC_URL%/favicon.ico" will
work correctly both with client-side routing and a non-root public URL.
Learn how to configure a non-root public URL by running `npm run build`.
-->
<title>React App</title>
</head>
<body>
<noscript>You need to enable JavaScript to run this app.</noscript>
<div id="root"></div>
<!--
This HTML file is a template.
If you open it directly in the browser, you will see an empty page.
You can add webfonts, meta tags, or analytics to this file.
The build step will place the bundled scripts into the <body> tag.
To begin the development, run `npm start` or `yarn start`.
To create a production bundle, use `npm run build` or `yarn build`.
-->
</body>
</html>

src/index.js

import React from "react"
import ReactDOM from "react-dom"
import "./index.css"
import App from "./App"
import reportWebVitals from "./reportWebVitals"
ReactDOM.render(
<React.StrictMode>
<App />
</React.StrictMode>,
document.getElementById("root")
)
const HelloWorld = () => <h1>Hello World</h1>
<div>
<HelloWorld />
</div>

There are some rules when it comes to JSX:

See the default react page

The app.js file

import logo from "./logo.svg"
import "./App.css"
function App() {
return <div className="App"></div>
}
export default App
import logo from "./logo.svg"
import "./App.css"
function App() {
const word = "Hello World"
return (
<div className="App">
<h1>{word}</h1>
</div>
)
}
export default App
const HelloWorld = () => <h1>Hello World</h1>function App() {
const word = "Hello World"
return (
<div className="App">
<HelloWorld />
</div>
)
}
import logo from "./logo.svg"
import "./App.css"
function App() {
const HelloWorld = () => <h1>Hello World</h1>
return (
<div className="App">
<HelloWorld />
</div>
)
}
export default App
import logo from "./logo.svg"
import "./App.css"
function App() {
const HelloWorld = props => <h1>{props.word}</h1>
return (
<div className="App">
<HelloWorld word="Hello World" />
</div>
)
}
export default App

State

import logo from "./logo.svg";
import "./App.css";
function App() { let count = 0 let addOne = () => {
console.log(count)
count += 1
}
return (
<div className="App">
<h1>{count}</h1>
<button onClick={addOne}>Add One To Count</button>
</div>
);
}
export default App;
import "./App.css";
import {useState} from "react"
function App() { // declare the new variable using useState which is passed the initial value
let [count, setCount] = useState(0)
let addOne = () => {
console.log(count)
setCount(count+1)
}
return (
<div className="App">
<h1>{count}</h1>
<button onClick={addOne}>Add One To Count</button>
</div>
);
}
export default App;

Seperation of concerns

import "./App.css";
import {useState} from "react"
const Counter = (props) => {
return (
<div className="App">
<h1>{props.count}</h1>
<button onClick={props.addOne}>Add One To Count</button>
</div>
);
}
function App() { // declare the new variable using useState which is passed the initial value
let [count, setCount] = useState(0)
let addOne = () => {
console.log(count)
setCount(count+1)
}
return <Counter count={count} addOne={addOne} />
}
export default App;

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Alex Merced Coder

Alex Merced is a Developer Advocate for Dremio and host of the Web Dev 101 and Datanation Podcasts.